In the field of electronic component assembly, sophisticated robotic manipulators are utilized to properly place electronic components on printed circuit boards. Robotic placement heads, under computer control, pick up components at supply stations, for example, by activation of a vacuum system on a spindle tip on the placement head. The placement head then moves to the correct programmed location in the X-Y coordinate system over the printed circuit board, the spindle and spindle tip are rotated to the correct theta or angular orientation, and the entire component placement head is moved downwardly in the Z direction to place the component on the board. Speed and accuracy are very important in such applications, particularly in what is known as surface mount applications where the component is placed on top of and is subsequently soldered or otherwise secured to elements on the top surface of the printed circuit board, as opposed to so-called through hole applications, where leads of the component are pushed through openings in the board. Due to the small size and sensitivity of the electronic components being surface mounted on the printed circuit board, it is critical that the electronic component not be pressed down too hard on the board. Thus, it is important to be able to determine the point where the component has been lowered the proper amount in the Z direction such that the component is in contact with the printed circuit board.
Prior art component placement systems utilized proximity sensors mounted to the spindle assembly, where the sensor had to move with the spindle assembly unit, and the associated electrical wiring for the sensors often gets tangled or damaged, resulting in reliability problems. These problems developed due to wire fatigue, problems associated with the wire guide structure, and related problems resulting from a sensor system that has moving wires.